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Comment by tsomctl | Hacker News Reader

Interesting. Presumably there will still be just piston rings in the normal place, although I would like to see more on how they are going to lubricate it. You don't want the gas spring chamber to fill up with oil. My guess for how they are going to get it started is by driving the permanent magnets with the coils. Also, why is it 2 stroke? I'd always assumed that 2 strokes were smaller and cheaper, but had less power. Possibly because there is no momentum to do 2 of the 4 strokes. Toyota definitely has the technology to make it a modern EFI 4 stroke, though. For the fuel intake and compression strokes, the coils could be disconnected from the load and driven so that the strokes complete.

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Two stroke engines are actually smaller, cheaper, and more powerful than four stroke engines of equal displacement. The issue with two stroke engines is cleanliness. Because there isn't a spare cycle to push all the extra unburned particles out of the chamber and let only clean air/fuel into the chamber, there is some loss of power efficiency due to the attempted combusting of leftover particles. This is more than mitigated by having double the amount of power strokes per equivalent displacement. There's actually some really interesting design techniques that have been used to "coax" the waste particles out of the chamber, take a look at MotoGP technology circa early 2000's if you want to learn more.

All the two stroke engines I have used (light aviation) have been terribly unreliable and painful to maintain. Won't start, often fires just on one cylinder, stops randomly, leaks oil everywhere. Is this a "shitty design" problem rather than an inherent problem with two-stroke engines?

Probably a combo of both. You know how I said above that there are some cool design techniques to get the old waste gases out of the cylinder? Well those techniques only work over a very narrow band of RPMs, under very specific air/fuel ratios. Your problem is even worse because you're in an aviation setting. Your engines are experiencing very different air densities, and this is causing the air/fuel ratio to change drastically compared to what they've been tuned for. If they get too rich, they stall. Too lean, they explode.

The leaky oil? Yeah, that's probably just a two stroke being a two stroke. Due to the design, they aren't "oiled" like a car, you instead shoot the oil in with the gasoline in the injection cycle, and it just kinda seeps in and around the engine. That's the main reason why they're dirty - both literally and environmentally.

Diesel engines have less problems when inlet air goes to the exhaust, since in a diesel, inlet air doesn't contain any fuel. A two stroke diesel has thus some synergistic advantages.

A direct injection otto engine could also work very well as a two stroke.

A bit of a tangential point, but two-stroke diesels also sound really awesome.

http://www.youtube.com/watch?v=C-oDw2iVcTk

http://www.youtube.com/watch?v=eEKlhdj7eEM

My bet would be that using a two-stroke cycle allows the piston to stay lubricated without using a sump for oil.

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